1. Field of the Invention
The present invention relates to a stencil printing apparatus having sheet re-feeding means so as to be capable of duplex printing.
2. Description of the Related Art
Digital thermal stencil printing is known in the related art as a simple printing method. In digital thermal stencil printing, a thermal head having a plurality of minute heat-generating elements is brought into contact with a master formed by adhering together a thermoplastic resin film and a porous support, and while pulse-form electrification is applied to the heat-generating elements, the master is conveyed by conveyance means such as a platen roller, whereby a perforated image based on image information is engraved by heat-melt punching on the thermoplastic resin film of the master. The engraved master is then wrapped around a porous cylindrical printing cylinder, and by pressing a sheet of paper against the outer peripheral surface of the printing cylinder using pressing means such as a press roller, ink supplied to the inner peripheral surface of the printing cylinder seeps through open hole portions in the printing cylinder and the perforated portions of the master so as to be transferred onto the sheet, whereby a printed image is formed on the sheet.
In the stencil printing described above, duplex printing, in which both surfaces of the sheet are printed, is performed with increasing frequency in recent times with a view to reducing paper consumption, document storage space and so on. As an example of this, Japanese Unexamined Patent Application Publication 2004-196476 discloses a stencil printing apparatus that uses a divided engraved master on which a first engraved image and a second engraved image are arranged in surface order in a rotation direction of a printing cylinder. One of the engraved images is printed on the front surface of a first sheet of paper fed by a sheet feeding unit, after which the sheet is guided to an auxiliary tray. One of the engraved images is then printed on the front surface of a second sheet of paper fed by the sheet feeding unit, whereupon the sheet is guided to the auxiliary tray. The first sheet is then re-fed from the auxiliary tray and the other engraved image is printed on the rear surface of the sheet, whereupon the sheet is discharged to a discharge tray. By performing this operation continuously, duplex printed matter is obtained in a single process.
In the stencil printing apparatus disclosed in the publication described above, the positions of the front surface image and rear surface image that are printed on the sheet can be adjusted individually by a predetermined amount. Here, when the positions of the images to be formed on the sheet are moved to an identical direction side in the sheet conveyance direction, the front surface side and rear surface side of the sheet move in opposite directions when the sheet is viewed from above, and therefore, if the front surface image is moved 3 mm toward the upstream side of the sheet conveyance direction, for example, setting must be performed to move the rear surface image 3 mm toward the downstream side in the sheet conveyance direction, and this setting is both troublesome and likely to be performed incorrectly. Further, even if the images are moved together to secure a binding margin or the like, for example, after the positions of the front surface image and rear surface image have been adjusted individually, positional adjustment must be performed on each image, and this operation is also troublesome.
Technologies relating to the present invention are also disclosed in, e.g. U.S. Pat. No. 6,718,872 (corresponding to Japanese Unexamined Patent Application Publication 2003-200645) and Japanese Unexamined Patent Application Publication 2003-237207.